This invention relates to procedure and compositions for non-destructive testing of bodies composed for example of metal, ceramic or plastic, or detect defects and metallurgical conditions in the surface of such bodies, and is particularly concerned with certain dry developer compositions for non-destructive dye penetrant inspection of parts, particularly employed in conjunction with certain dye penetrants, the powder developers of the invention being particularly effective in providing bright, e.g. fluorescent, indications, and having additional important advantages and superior results in comparison with presently known and commerically available powder developers.
In known penetrant inspection methods for rapid location and evaluation of surface flaws, defects or cracks in test bodies or parts, a penetrant composition containing a fluorescent dye and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition is then applied to the part surface. Such developer can be in the form of a light colored powder, which contrasts with the color of the dye and which acts as a wick and causes the liquid penetrant containing the fluorescent dye which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action, and to "bleed" through the developer. Excess developer is removed and the part is then exposed to invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
In order to increase the sensitivity of fluorescent penetrant inspection methods, it has been sought to increase the brightness of fluorescence of the fluorescent penetrant dye and to increase the contrast between the light received from the fluorescent penetrant indicator and from adjacent areas of the test part, thereby obtaining increased sensitivity.
Various developer compositions for penetrant inspection of surface cracks and flaws have heretofore been employed. Thus, for example, U.S. Pat. No. 2,806,959 discloses finely powdered silica, preferably admixed with talc in a proportion of 80% silica and 20% talc; U.S. Pat. No. 2,848,421 discloses a composition comprising silica aerogel and talc; and my U.S. Pat. No. 3,803,051 discloses an improved developer composition consisting essentially of alumina, titanium dioxide, talc and silica, the latter employed in relatively small amounts ranging from about 2 to 25%, e.g. about 4 or 5% by weight.
However, most of the dry developer compositions of the prior art have the disadvantage that when excess dry developer is removed from a part surface by air blasting, a common method of removing excess developer prior to inspection of the developer treated surface, a substantial amount of the developer in the cracks adjacent the part surface, and containing liquid penetrant drawn into the developer from such cracks, is also removed, and hence in effect reducing the sensitivity and brightness of fluorescence of the fluorescent dye in the cracks and defects.
Further, many of the prior art developer compositions tend to agglomerate and cake and hence this reduces their sensitivity to penetrant inspection of very small cracks or microcracks in the surface being tested.
Further, certain of the prior art developer compositions are not compatible with certain metals such as titanium and high nickel alloys which are used particularly in the aerospace industry, because such compositions contain elements or components such as chlorine and sulfur, so that the resulting composition has a low pH when contacted by the liquid penetrant.
Also, some of the prior art compositions are toxic and hence present hazards in handling.
In my copending applications Ser. Nos. 444,432 now U.S. Pat. 3890007 and 444,433, now abandoned both filed Feb. 21, 1974, now Patent Nos. 3,915,885 and 3,915,886, respectively, there is disclosed novel dye penetrants which have improved washability and sensitivity characteristics, and which are biodegradable, containing as the vehicle for the dye, certain biodegradable nonionic oxyalkylated alcohols.
It is accordingly an object of the present invention to provide a simple dry developer composition particularly useful for fluorescent dye penetrant inspection of the surface cracks and defects of bodies, comprising a minimum of components, and which provides high sensitivity, bright fluorescence and sharp contrast between the light emitted from the fluorescent penetrant indicating the location and nature of cracks and imperfections in the body, and the adjacent areas of the part, particularly when employed in a dye penetrant inspection process in conjunction with a dye penetrant containing as vehicle for the dye certain biodegradable nonionic oxyalkylated alcohols, as disclosed in my above copending applications. Another object is the provision of a dry developer for dye penetrant inspection as described above, and having other important advantages including light free-flowing characteristics, compatibility with structural materials such as metals and alloys thereof, and which are essentially nontoxic and relatively inexpensive.